Proximity communication systems using various non-contact ICs have been currently employed in a wide range of fields. In such communication systems, for example, a non-contact IC card or a non-contact IC tag comes close to a card reader within a predetermined distance to perform near-field radio communication. There have been devised non-contact IC cards or non-contact IC tags including a module in which a wireless communication IC functioning as a data carrier is integrated with an antenna.
For example, JP 4788850 B2 and WO 2010/087429 describe an antenna module that includes an electromagnetic coupling module having a wireless communication IC and a power supply coil connected to the wireless communication IC, and an antenna that has a first coil electrode wound along a first principal surface of an insulating base and a second coil electrode wound along a second principal surface opposing the first principal surface. In the antenna, openings of the first coil electrode and the second coil electrode can be made larger than an opening of the power supply coil of the electromagnetic coupling module. This increases the magnetic flux linking an antenna coil of a communication target. In other words, the antenna functions as not only an antenna resonance circuit but also a booster antenna for the electromagnetic coupling module.
The degree of coupling of the booster antenna and the power supply coil of the electromagnetic coupling module (i.e., an RFIC module) influences the amount of magnetic field energy received by the wireless communication IC via the booster antenna and thus is preferably as high as possible. A higher degree of coupling allows for a longer communication distance in the communication systems. To increase the degree of coupling, the antenna modules described in JP 4788850 B2 and WO 2010/087429 increase the number of windings of a coupling part of the booster antenna performing electromagnetic field coupling to the power supply coil of the electromagnetic coupling module. Additionally, the electromagnetic coupling module is mounted on the booster antenna so that the power supply coil of the electromagnetic coupling module overlaps the coupling part.
The resonance frequencies of a booster antenna and an RFIC module (an RFIC element and a power supply coil connected to the RFIC element) are set as the communication frequency. Unfortunately, if the mounting position of the electromagnetic coupling module (the RFIC module) is shifted relative to the coupling part of the booster antenna in the structures described in JP 4788850 B2 and WO 2010/087429, the capacity between, or the degree of coupling of, the coupling part of the booster antenna and the power supply coil may change. The resonance frequency is set by the inductance (the inductive reactance) and the capacity (the capacitive reactance) of a circuit. When the capacity between, or the degree of coupling of, the coupling part of the booster antenna and the power supply coil changes, the resonance frequencies of the booster antenna and the RFIC module may also change. These resonance frequencies deviate from the communication frequency for communication and thus the degree of coupling to an antenna coil of a communication target decreases, reducing a communication distance in communication systems.
The electromagnetic coupling module (the RFIC module) is mounted on an insulating base in the structures described in JP 4788850 B2 and WO 2010/087429, and thus the thickness of an antenna module increases. A cavity may be formed in the insulating base and the electromagnetic coupling module may be accommodated in the cavity. However, this complicates the structure of the antenna module and requires a step of forming the cavity in the insulating base, so that a manufacturing process is also complicated.